Hi, Jose. Thank you for your response. The application note was very interesting and helpful.
The problem seems to be related to the heatsink. We are using the 8954J (through-hole) version with an Aavid 530101B00150G heatsink. We were originally using some thermal grease between the part and the heatsink, but the thickness was too thick and very variable. We are now using some Bergquist Sil-Pad, so the problem is very similar across different boards.We are also seeing shutdown with low supply voltages, like +/-32V, so I am very suspicious about the heatsink.
My production engineer has discovered that he can make the problem go away but raising the heatsink up off the board. This suggests to me that there is some coupling between the circuit board and the heatsink. The data sheet for the 8954 says that the heat spreader is at VSS and to use a 0.1uf cap to either ground or VSS, so I would think that this "decouples" the heatsink from any noise emanating from the board. The output traces run directly underneath the heatsink, but moving them to the underside of the board does not help.
The cap at the PROT pin seems very sensitive. If I increase it about 10pf, say to 100pf, the problem becomes very bad.
I am very confused, so any thoughts you might have would be very helpful.
